Chemical, pharmaceutical and semiconductor processes are typically performed in a process chamber under vacuum conditions. The process chamber is evacuated by a vacuum pump of appropriate capacity. Such a vacuum pump may for example be a single stage booster or multi stage pump of Roots or Northey (“claw” type) configuration, alternatively the pumping mechanism may have a single or multi stage screw mechanism.
Many of the above processes use or generate potentially flammable mixtures containing a fuel such as an organic solvent, hydrogen or silane. The pumping of such mixtures requires great care to be placed on the leak integrity of the foreline and exhaust lines from the pump to ensure that there is no ingress of air into the lines which could create a flammable atmosphere. Moreover, in some processes a fuel and an oxidant, for example TEOS (tetraethoxysilane) and ozone, may flow through the pump at the same time. In such circumstances any hot spots within the pump could provide intermittent ignition sources for the fuel, which could result in the generation of hazardous flame fronts travelling through the pump into the exhaust lines, or, where explosion pressures are sufficiently high, into the process chamber.
Management of risks associated with such potentially hazardous installations are governed by industry Standards. Different classifications of risk can be specified by these Standards, each class requiring different levels of subsidiary safety devices, instrumentation and or controls to be employed in order to mitigate the different perceived levels of risk associated with that particular class. Equipment may be given a higher classification due to potential risk that may in practical terms be rarely achieved. This additional mitigation equipment may only be actively utilised during exceptional, hazardous circumstances, being effectively redundant during normal operation of the pump. Such redundancy, in many applications, can be detrimental to the overall capacity of the pumping apparatus either due to the cost of, or additional space required to accommodate, such redundant equipment. It is, therefore, desirable to provide alternative mitigation techniques that minimise the costs and footprint of such mitigation equipment. One example of such mitigation equipment is a flame arrester, which causes a significant pressure drop in the fluid passing therethrough. When such a flame arrester is placed at the inlet of the pump, i.e. in a region that is particularly sensitive to such pressure drops, the pumping performance of the vacuum pump can be significantly affected.